def calc_mean(numbers):
    sum1 = 0
    for x in numbers:
        sum1 += x
    if sum1 != 0:
        return sum1/len(numbers)
    return float(sum1)

assert calc_mean([5, 7, 1, 3]) == 4.0
assert calc_mean([12, 37, 41]) == 30.0
assert calc_mean([6, 5]) == 5.5
assert calc_mean([0]) == 0.0